JAMB Chemistry Past Questions & Answers - Page 432

2,156.

In which of the following are water molecules in the most disorderly arrangement?

Ice at -10°C

Ice at 0°C

Water at 100°C

Steam at 100°C

Correct answer is D

The gaseous state of matter has the most disorderly arrangement of particles. Hence, steam (water in gaseous form) is the most disorderly arrangement on the list.

2,157.

A gaseous metallic chloride MClx consists of 20.22% of M by mass. The formula of the chloride is?
[M = 27, Cl = 35.5]

MCl

MCl₂

MCl₃

M₂Cl₆

View answer & explanation

Correct answer is C

Percentage by mass of M = 20.22%
Percentage by mass of Cl = ?
100 - 20.22 = 79.78%
Mass given ration of M
M = 20.22/27 = 0.75
Chlorine = 79.78/35.5 = 2.24
Divide by the smallest
M = 0.75/0.75 = 1
Cl = 2.24/0.75 = 3
∴ The formula = MCl3

2,158.

Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g)
From the equation above, the mass of magnesium required to react with 250cm3 of 0.5M HCl is
[Mg = 24]

0.3g

1.5g

2.4g

3.0g

View answer & explanation

Correct answer is B

Molar conc. =no.of moles／Vol in dm3
Vol=250cm3= 0.25dm3
Molar conc=0.5M
No of moles=molar conc *Vol in dm3
=0.5*0.25
=0.125mole of HCl
2moles of HCl → １Mole of Mg
0.125 mole →(0.125*1)/2
=0.0625mole of Mg
Reacting mass=no of moles* molar mass
Mg=24
Mass=0.0625*24
=1.5g